Re: [QEMU PATCH 1/1] virtgpu: do not destroy resources when guest suspend

[Gerd Hoffmann]

On Tue, Jun 20, 2023 at 01:26:15PM +0100, Robert Beckett wrote:
> 
> On 20/06/2023 10:41, Gerd Hoffmann wrote:
> >    Hi,
> > 
> > > > The guest driver should be able to restore resources after resume.
> > > Thank you for your suggestion!
> > > As far as I know, resources are created on host side and guest has no 
> > > backup, if resources are destroyed, guest can't restore them.
> > > Or do you mean guest driver need to send commands to re-create resources 
> > > after resume?
> > The later.  The guest driver knows which resources it has created,
> > it can restore them after suspend.
> 
> Are you sure that this is viable?
> 
> How would you propose that a guest kernel could reproduce a resource,
> including pixel data upload during a resume?
> 
> The kernel would not have any of the pixel data to transfer to host.

Depends on the of resource type.  For resources which are created by
uploading pixel data (using VIRTIO_GPU_CMD_TRANSFER_TO_HOST_*) a guest
mirror exists which can be used for re-upload.

For resources filled by gl rendering ops this is indeed not the case.

> Could you explain how you anticipate the guest being able to reproduce the
> resources please?

Same you do on physical hardware?  Suspend can poweroff your PCI
devices, so there must be some standard way to handle that situation
for resources stored in gpu device memory, which is very similar to
the problem we have here.

take care,
  Gerd